CAN communication between 3 Nucleo boards

Srivatsan · ‎2026-02-10

Hi,

I am trying to establish CAN communication between three different MCUs: NUCLEO-H723ZG, NUCLEO-H755ZIQ, and NUCLEO-G474RE. However, I am unable to successfully communicate between the boards, even though the same baud rate has been configured on all MCUs. I have also connected an external CAN transceiver to each board for proper CAN bus operation.

On the NUCLEO-G474RE, I have enabled UART4 to send command data, using the following pins:

PC11 – UART4_RX
PC10 – UART4_TX

Clock Frequency [SYSCLK] & Baud Rate [CAN]:

1. NUCLEO-H723ZG: 550 MHz

Baud Rate: 500000 Bit/s

2. NUCLEO-H755ZIQ: 480 MHz

Baud Rate: 500000 Bit/s

3. NUCLEO-G474RE: 170 MHz

Baud Rate: 500000 Bit/s

mƎALLEm · ‎2026-02-13

I don't know what you did behind the scene. What Channel 1 refers to? G4 FDCAN Tx? or CAN analyzer Tx?

If one of them, H7 FDCAN_Rx is not receiving anything, so it's a hardware issue either a wiring issue or a transceiver issue.

- So check your wiring on H7 side

- Check the power supply of your transceiver

- Even, replace the transceiver used by STM32H7.

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Ozone · ‎2026-02-10

Have you used a scope to see what is happening on the CAN bus ?

Have you checked the CAN_Tx pins from the MCUs to the transceiver, if you see a signal ?

What do the TEC and REC counter values of the CAN peripheral say ?

> On the NUCLEO-G474RE, I have enabled UART4 to send command data, using the following pins: ...

How is this relevant here ?

Andrew Neil · ‎2026-02-10

@Srivatsan wrote:
I have also connected an external CAN transceiver to each board

What CAN transceiver?

Please show your schematic of how you connected the transceiver to the Nucleo board, and how you have the transceivers connected to each other.

Some good, clear photos of your setup could help.

How to write your question to maximize your chances to find a solution

Simple Classic CAN + FreeRTOS Demo simulating OBD and a vehicle

Guide to CAN (bxCAN/CAN2.0) configuration in Loop back mode on STM32 MCUs - with links to more examples at the end.

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

mƎALLEm · ‎2026-02-10

Hello,

Many info are missing.

1-You need to tell what the problem is? on which side? on transmit or on receive?

"However, I am unable to successfully communicate between the boards" does tell nothing.

2- Please describe what you've did at this stage to debug the issue and show your CAN bus diagram in this way:

3- What transceiver are you using? and show your hardware schematic.

PS1: avoid using HSI for CAN and use external precise clock source such as a crystal. Here you are using HSI for G4 project! and avoid setting 1tq for one of the time bit segments:

PS2: please attach the ioc files instead of sharing screenshots of your CubeMx config

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Srivatsan · ‎2026-02-10

I am using UART4 on the NUCLEO-G474RE to send command inputs along with the target address for toggling GPIO pins.

All three MCUs are connected through a CAN bus network. When a command is sent via UART4, the G474RE acts as the CAN master and transmits the corresponding CAN message to the other MCUs to control their GPIO outputs.

Each board is interfaced with a TJA1050 CAN transceiver for proper CAN communication.

Example use case:
If I send a command from the G474RE board to toggle a specific GPIO on the NUCLEO-H723ZG, the targeted GPIO pin should turn ON or OFF accordingly.

VCC is connected to the 5V
GND is connected to the GND pin of the board

NUCLEO-G474RE (0x100) - Led Pin no: PA5 (acts as Master)

PA12 - FDCAN1_TX

PA11 - FDCAN1_RX

PC11 - UART4_RX

PC10 - UART4_TX

NUCLEO-H723ZG (0x101) - Led Pin no: PB0

PA12 - FDCAN1_TX

PA11 - FDCAN1_RX

NUCLEO-H755ZIQ (0x102) - Led Pin no: PB0

PD1 - FDCAN1_TX

PD0 - FDCAN1_RX

mƎALLEm · ‎2026-02-10

You need to simplify your test and make a simple communication without any command sent from the PC, that complicates things and (at this level) we don't know what the problem is?

Please make a simple project where only CAN communication is done. So please remove the UART and other stuff.

PS3: you didn't answer all my questions above.

PS4: what about S pin level of the trancveiver?

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Ozone · ‎2026-02-10

> When a command is sent via UART4, the G474RE acts as the CAN master and transmits the corresponding CAN message to the other MCUs to control their GPIO outputs.

There is no such thing as a "CAN master".

Check the bus signal(s), and post the result.

LCE · ‎2026-02-10

Got 2 120R termination resistors on the bus?

But even more important: make it more simple at first:

- start with only 1 MCU, if possible get some known & working USB / CAN adapter

- use a scope to check that your initial message gets out of the sender

- do not use BRS in the beginning

I you have each MCU's CAN running on its own, then you can start connecting these.

mƎALLEm · ‎2026-02-10

@LCE wrote:

Got 2 120R termination resistors on the bus?

But even more important: make it more simple at first:

- start with only 1 MCU, if possible get some known & working USB / CAN adapter

- use a scope to check that your initial message gets out of the sender

I you have each MCU's CAN running on its own, then you can start connecting these.

Totally agree with this.

@LCE wrote:

- do not use BRS in the beginning

He's using Classic CAN mode. No need for BRS.

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mƎALLEm · ‎2026-02-10

I've just noticed this configuration:

That's a bad configuration.TSEG1 =TSEG2 = Tq!

You need to avoid such timing configuration and you need to position the sample point at about 87.5%. Decrease the the nominal prescaler and increase TSEG1 and TSEG2 values as much as possible with the proposed sample point.

Read this article: CAN (bxCAN) bit time configuration on STM32 MCUs . It treats bxCAN but applies also to FDCAN in Classic mode.

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